1. Field of the Invention
The present invention relates to disk drives for computer systems. More particularly, the present invention relates to a disk drive determining a head-switch preheat period used to format a disk.
2. Description of the Prior Art
In disk drives, a head is actuated radially over a disk in order to access a target track recorded on the disk. The head is attached to a distal end of an actuator arm which is rotated about a pivot by a voice coil motor during seek operations. As the disk rotates, an air bearing forms which causes the head to “fly” just above the disk surface while writing magnetic transitions during a write operation, or reading the magnetic transitions during a read operation. The head comprises a slider having an air bearing surface and an integrated transducer, such as a write coil and a magnetoresistive read element.
Decreasing the distance between the transducer and disk surface (fly-height) improves the signal-to-noise ratio in the read signal, thereby enabling higher recording densities (radial tracks per inch and linear bits per inch). To this end, designers have exploited the thermal expansion properties of the head (e.g., the slider and/or transducer) by incorporating a heater to control the temperature of the head and thereby the fly-height. Increasing the temperature causes the head to expand, thereby moving the transducer closer to the disk surface.
Prior art disk drives typically employ multiple heads (e.g., top and bottom heads) and may also employ multiple disks with corresponding top and bottom heads. Typically only one head is active at a time for accessing data sectors recorded in tracks of the corresponding disk surface. When the disk drive performs a head-switch to access a different disk surface, the preheat period required to heat the newly selected head can result in a slipped revolution if the head does not attain an acceptable fly-height prior to reaching the target data sector.
There is, therefore, a need to decrease the fly-height in a disk drive by heating the head without increasing the access time of the disk drive during a head-switch operation.